A power-module substrate with a heat sink is used for a power module for a vehicle, in which aluminum plates are joined on a ceramic substrate including aluminum nitride or the like, and an aluminum-based heat sink is joined on one side with the aluminum plate therebetween.
Such a power-module substrate with a heat sink is conventionally manufactured as followings. First, two aluminum plates are stacked on two surfaces of a ceramic substrate with interposing brazing material which is suitable for bonding the ceramic substrate and the aluminum plates therebetween, heating them to a temperature melting the brazing material or higher with pressing them at a prescribed pressure force, so that the ceramic substrate and the aluminum plates on both the surfaces are bonded. Next, on one of the aluminum plates, a heat sink is stacked with interposing brazing material which is suitable for bonding the aluminum plate and the heat sink therebetween, heating them to a temperature melting the brazing material or higher with pressing them at a prescribed pressure force, so that the aluminum plate and the heat sink are bonded. Thereby, manufacturing the power-module substrate with the heat sink.
In the above-mentioned power-module substrate with a heat sink, one of the aluminum plates is formed as a circuit layer on which semiconductor elements such as a power element and a like are mounted with interposing solder material.
In the above-mentioned power-module substrate, it is necessary that a warp be small because a heat radiation property and the like are deteriorated if there is a warp.
Conventionally, there are arts described in Patent Documents 1 and 2 for example as arts for reducing a warp and the like of a power-module substrate.
A power-module substrate described in Patent Document 1 is provided with a metal plate as a circuit layer made of a clad material. The clad material is formed by stacking two or more layers including a first layer with an aluminum purity of 99.0 mass % to 99.95 mass % inclusive and a second layer with an aluminum purity of 99.99 mass % or higher. The second layer is bonded on a ceramic substrate. It is described that a circuit layer thickness is 600 μm and a metal layer to be provided at a back surface to the circuit layer of the ceramic substrate has a thickness of 400 μm.
Patent Document 2 discloses a silicon nitride circuit substrate in which a metal clad material is bonded on at least one of surfaces of a silicon nitride substrate. It is also disclosed that a combination of an electric conductive material such as a Cu plate, Al plate and the like and a low thermal-expansion metal such as a kovar plate, a tungsten plate and the like is suitable as the metal clad material.